The term “β-glucan” refers to those polysaccharides which comprise D-glucopyranosyl units which are linked together by (1→3) or (1→4) β-linkages. β-Glucans occur naturally in many cereal grains such as oats and barley. The molecular weight of β-glucan molecules occurring in cereals is typically 200 to 2000 kiloDaltons.
β-Glucan is desirable as a food additive, for example, to impart texture (“mouth feel”) to foods or useful as edible films for food coatings. β-Glucan may also be used to add bulk to foods and has the advantage of having a neutral flavour.
β-Glucan is also desirable as a therapeutic agent. There is evidence that β-glucan can lower serum cholesterol levels, heal wounds, moderate glycaemic response, and alleviate constipation. β-Glucan can actively bind to specific cell receptors and therefore may be useful for the treatment of a wide variety of disorders or diseases.
The known methods for extracting β-glucan from cereal grains, such as oats and barley, involve several steps. Firstly, the cereal grain is milled to a flour prior to extracting β-glucan from the flour using warm or hot water or an aqueous alkali solution. The milling step facilitates release of the β-glucan from the cereal. The aqueous extract of β-glucan is then separated from the solid flour residue. Finally, the β-glucan is recovered from the extract.
The known methods of recovering the β-glucan from the aqueous extract include precipitation of the β-glucan using a water miscible solvent, such as alcohol, or by freezing and then thawing the extract to give a precipitate of β-glucan which can be recovered by filtration or centrifugation. The extraction of the β-glucan itself from the cereal is not generally a costly process. However, the recovery of the β-glucan from the extract is costly. This is due to the large amounts of water that must be removed to give solid β-glucan.
In addition, it is difficult to control the molecular weight of the β-glucan product obtained from known processes. High molecular weight β-glucan is preferable for certain uses. For example, high molecular weight β-glucan is preferable for moderating glycaemic response and for lowering serum cholesterol levels. On the other hand, low molecular weight β-glucan may be preferable as a food additive. For example, low molecular weight β-glucan can form a gel having beneficial textural properties for processed foods.
In order to obtain a high molecular weight β-glucan product, previous methods of β-glucan extraction from cereals have required that enzymes present in the cereal be deactivated prior to the extraction step. The enzymes are responsible for lowering β-glucan molecular weight and are deactivated either by treating the flour with boiling ethanol/water mixtures or by treating the flour with an aqueous acid solution.